Signaling methods for MMSE precoding with eigenmode selection

ABSTRACT

Different methods of signaling between an access point and user terminals in a multiuser wireless system for performing a minimum mean square error (MMSE) precoding at the access point preceded with eigenmode selection are provided. For one embodiment of the present disclosure, a compact feedback may be utilized between a plurality of user terminals and the access point. For another embodiment of the present disclosure, a hybrid feedback may be utilized between the plurality of user terminals and the access point. For yet another embodiment of the present disclosure, a full feedback may be utilized between the plurality of user terminals and the access point.

TECHNICAL FIELD

The present disclosure generally relates to communication, and morespecifically to a signaling between an access point and user terminalsin a multiuser wireless system for performing a minimum mean squareerror (MMSE) preceding at the access point preceded with eigenmodeselection.

BACKGROUND

In order to address the issue of increasing bandwidth requirementsdemanded for wireless communication systems, different schemes are beingdeveloped to allow multiple user terminals to communicate with a singleaccess point by sharing the same channel (same time and frequencyresources) while achieving high data throughputs. Spatial DivisionMultiple Access (SDMA) represents one such approach that has recentlyemerged as a popular technique for the next generation communicationsystems. SDMA techniques may be adopted in several emerging wirelesscommunications standards such as IEEE 802.11 (IEEE is the acronym forthe Institute of Electrical and Electronic Engineers, 3 Park Avenue,17th floor, New York, N.Y.) and Long Term Evolution (LTE).

In SDMA systems, an access point may transmit or receive differentsignals to or from a plurality of user terminals at the same time andusing the same frequency. In order to achieve reliable datacommunication, signals dedicated to different user terminals may need tobe mutually orthogonal and located in sufficiently different directions.Independent signals may be simultaneously transmitted from each ofmultiple space-separated antennas at the access point. Consequently, thecombined transmissions may be mutually orthogonal and/or directional;i.e., the signal that is dedicated for each user terminal may berelatively strong in the direction of that particular user terminal, andsufficiently weak in directions of other user terminals. Similarly, theaccess point may simultaneously receive on the same frequency thecombined signals from multiple user terminals through each of multipleantennas separated in space, and the combined received signals from themultiple antennas may be split into independent signals transmitted fromeach user terminal by applying the appropriate signal processingtechnique.

A multi-antenna communication system employs multiple transmit antennasat a transmitting entity and one or more receive antennas at a receivingentity for data transmission. The multi-antenna communication system maythus be a multiple-input multiple-output (MIMO) system. The MIMO systememploys multiple (N_(t)) transmit antennas and multiple (N_(r)) receiveantennas for data transmission. A MIMO channel formed by the N_(t)transmit antennas and the N_(r) receive antennas may be decomposed intoN_(sh) spatial channels, where N_(sh)≦min {N_(t), N_(r)}. The N_(sh)spatial channels may be used to transmit N_(sh) independent data streamsin a manner to achieve greater overall throughput.

In a multiple-access MIMO system based on SDMA, an access point cancommunicate with one or more user terminals at any given moment. If theaccess point communicates with a single user terminal, then the N_(t)transmit antennas are associated with one transmitting entity (eitherthe access point or the user terminal), and the N_(r) receive antennasare associated with one receiving entity (either the user terminal orthe access point). The access point can also communicate with multipleuser terminals simultaneously via SDMA. In general, for SDMA, the accesspoint utilizes multiple antennas for data transmission and reception,and each of the user terminals typically utilizes less than the numberof access point antennas for data transmission and reception.

Good performance (e.g., high transmission capacity and low error rate)can be achieved by transmitting data on eigenmodes of MIMO channelsbetween the access point and every individual user terminal. Theeigenmodes may be viewed as orthogonal spatial channels. Thetransmission on eigenmodes may provide decreased inter-userinterference, as well as decreased interference between differentspatial streams simultaneously transmitted from the access pointantennas and dedicated to a single user terminal. Every user terminalmay estimate a MIMO channel response, perform singular-valuedecomposition of the channel matrix, select one or more most reliableeigenmodes (i.e., eigenmodes with the largest eigenvalues), and send tothe access point via feedback the corresponding quantized eigenvectorsalong with related eigenvalues and channel quality information (CQI).The access point may then generate the precoding matrix and performspatial processing (beamforming) using the generated precoding matrix inorder to multiplex data to different user terminals with reducedinter-user interference.

Therefore, there is a need in the art for efficient signaling in themultiuser wireless system between the access point and user terminals.

SUMMARY

Certain embodiments provide a method for signaling in a multiuserwireless communication system with compact feedback. The methodgenerally includes sending to a plurality of user terminals a predefinedtraining sequence indicating a maximum number of spatial streams foreach of the user terminals to send feedback, and receiving via feedbackchannels from each of the user terminals a quantized version of selectedeigenvectors, corresponding quantized eigenvalues, and quantized channelquality information (CQI).

Certain embodiments provide a method for signaling in a multiuserwireless communication system with compact feedback. The methodgenerally includes estimating a channel between an access point and auser terminal based on a received training sequence, performing asingular value decomposition to compute eigenvalues and eigenvectors ofthe estimated channel, and selecting up to a specified number of mostreliable eigenmodes to be fed back to the access point.

Certain embodiments provide a method for signaling in a multiuserwireless communication system with hybrid feedback. The method generallyincludes estimating full uplink channels based on a sounding sequencesreceived from a plurality of user terminals, estimating a downlinkchannel between the access point and each of the user terminals assumingreciprocity of corresponding uplink and downlink channels, computingeigenvalues and eigenvectors of estimated downlink channels, andselecting most reliable eigenmodes up to a predefined number perdownlink channel between the access point and each of the userterminals.

Certain embodiments provide a method for signaling in a multiuserwireless communication system with hybrid feedback. The method generallyincludes transmitting a sounding sequence along with explicit datacarrying a quantized version of estimated Channel Quality Information(CQI) at a user terminal.

Certain embodiments provide a method for signaling in a multiuserwireless communication system with full feedback. The method generallyincludes transmitting a predefined training sequence, computingeigenvalues and eigenvectors of estimated downlink channels, andselecting most reliable eigenmodes up to a predefined number perdownlink channel between an access point and every individual userterminal.

Certain embodiments provide a method for signaling in a multiuserwireless communication system with full feedback. The method generallyincludes estimating a channel between an access point and a userterminal based on a received training sequence, and transmitting aquantized version of a normalized full downlink channel matrix and aquantized version of estimated channel quality information (CQI).

Certain embodiments provide an apparatus for signaling in a multiuserwireless communication system with compact feedback. The apparatusgenerally includes logic for sending to a plurality of user terminals apredefined training sequence indicating a maximum number of spatialstreams for each of the user terminals to send feedback, and logic forreceiving via feedback channels from each of the user terminals aquantized version of selected eigenvectors, corresponding quantizedeigenvalues, and quantized channel quality information (CQI).

Certain embodiments provide an apparatus for signaling in a multiuserwireless communication system with compact feedback. The apparatusgenerally includes logic for estimating a channel between an accesspoint and a user terminal based on a received training sequence, logicfor performing a singular value decomposition to compute eigenvalues andeigenvectors of the estimated channel, and logic for selecting up to aspecified number of most reliable eigenmodes to be fed back to theaccess point.

Certain embodiments provide an apparatus for signaling in a multiuserwireless communication system with hybrid feedback. The apparatusgenerally includes logic for estimating full uplink channels based on asounding sequences received from a plurality of user terminals, logicfor estimating a downlink channel between the access point and each ofthe user terminals assuming reciprocity of corresponding uplink anddownlink channels, logic for computing eigenvalues and eigenvectors ofestimated downlink channels, and logic for selecting most reliableeigenmodes up to a predefined number per downlink channel between theaccess point and each of the user terminals.

Certain embodiments provide an apparatus for signaling in a multiuserwireless communication system with hybrid feedback. The apparatusgenerally includes logic for transmitting a sounding sequence along withexplicit data carrying a quantized version of estimated Channel QualityInformation (CQI) at a user terminal.

Certain embodiments provide an apparatus for signaling in a multiuserwireless communication system with full feedback. The apparatusgenerally includes logic for transmitting a predefined trainingsequence, logic for computing eigenvalues and eigenvectors of estimateddownlink channels, and logic for selecting most reliable eigenmodes upto a predefined number per downlink channel between an access point andevery individual user terminal.

Certain embodiments provide an apparatus for signaling in a multiuserwireless communication system with full feedback. The apparatusgenerally includes logic for estimating a channel between an accesspoint and a user terminal based on a received training sequence, andlogic for transmitting a quantized version of a normalized full downlinkchannel matrix and a quantized version of estimated channel qualityinformation (CQI).

Certain embodiments provide an apparatus for signaling in a multiuserwireless communication system with compact feedback. The apparatusgenerally includes means for sending to a plurality of user terminals apredefined training sequence indicating a maximum number of spatialstreams for each of the user terminals to send feedback, and means forreceiving via feedback channels from each of the user terminals aquantized version of selected eigenvectors, corresponding quantizedeigenvalues, and quantized channel quality information (CQI).

Certain embodiments provide an apparatus for signaling in a multiuserwireless communication system with compact feedback. The apparatusgenerally includes means for estimating a channel between an accesspoint and a user terminal based on a received training sequence, meansfor performing a singular value decomposition to compute eigenvalues andeigenvectors of the estimated channel, and means for selecting up to aspecified number of most reliable eigenmodes to be fed back to theaccess point.

Certain embodiments provide an apparatus for signaling in a multiuserwireless communication system with hybrid feedback. The apparatusgenerally includes means for estimating full uplink channels based on asounding sequences received from a plurality of user terminals, meansfor estimating a downlink channel between the access point and each ofthe user terminals assuming reciprocity of corresponding uplink anddownlink channels, means for computing eigenvalues and eigenvectors ofestimated downlink channels, and means for selecting most reliableeigenmodes up to a predefined number per downlink channel between theaccess point and each of the user terminals.

Certain embodiments provide an apparatus for signaling in a multiuserwireless communication system with hybrid feedback. The apparatusgenerally includes means for transmitting a sounding sequence along withexplicit data carrying a quantized version of estimated Channel QualityInformation (CQI) at a user terminal.

Certain embodiments provide an apparatus for signaling in a multiuserwireless communication system with full feedback. The apparatusgenerally includes means for transmitting a predefined trainingsequence, means for computing eigenvalues and eigenvectors of estimateddownlink channels, and means for selecting most reliable eigenmodes upto a predefined number per downlink channel between an access point andevery individual user terminal.

Certain embodiments provide an apparatus for signaling in a multiuserwireless communication system with full feedback. The apparatusgenerally includes means for estimating a channel between an accesspoint and a user terminal based on a received training sequence, andmeans for transmitting a quantized version of a normalized full downlinkchannel matrix and a quantized version of estimated channel qualityinformation (CQI).

Certain embodiments provide a computer-program product for signaling ina multiuser wireless communication system with compact feedback,comprising a computer readable medium having instructions storedthereon, the instructions being executable by one or more processors.The instructions generally include instructions for sending to aplurality of user terminals a predefined training sequence indicating amaximum number of spatial streams for each of the user terminals to sendfeedback, and instructions for receiving via feedback channels from eachof the user terminals a quantized version of selected eigenvectors,corresponding quantized eigenvalues, and quantized channel qualityinformation (CQI).

Certain embodiments provide a computer-program product for signaling ina multiuser wireless communication system with compact feedback,comprising a computer readable medium having instructions storedthereon, the instructions being executable by one or more processors.The instructions generally include instructions for estimating a channelbetween an access point and a user terminal based on a received trainingsequence, instructions for performing a singular value decomposition tocompute eigenvalues and eigenvectors of the estimated channel, andinstructions for selecting up to a specified number of most reliableeigenmodes to be fed back to the access point.

Certain embodiments provide a computer-program product for signaling ina multiuser wireless communication system with hybrid feedback,comprising a computer readable medium having instructions storedthereon, the instructions being executable by one or more processors.The instructions generally include instructions for estimating fulluplink channels based on a sounding sequences received from a pluralityof user terminals, instructions for estimating a downlink channelbetween the access point and each of the user terminals assumingreciprocity of corresponding uplink and downlink channels, instructionsfor computing eigenvalues and eigenvectors of estimated downlinkchannels, and instructions for selecting most reliable eigenmodes up toa predefined number per downlink channel between the access point andeach of the user terminals.

Certain embodiments provide a computer-program product for signaling ina multiuser wireless communication system with hybrid feedback,comprising a computer readable medium having instructions storedthereon, the instructions being executable by one or more processors.The instructions generally include instructions for transmitting asounding sequence along with explicit data carrying a quantized versionof estimated Channel Quality Information (CQI) at a user terminal.

Certain embodiments provide a computer-program product for signaling ina multiuser wireless communication system with full feedback, comprisinga computer readable medium having instructions stored thereon, theinstructions being executable by one or more processors. Theinstructions generally include instructions for transmitting apredefined training sequence, instructions for computing eigenvalues andeigenvectors of estimated downlink channels, and instructions forselecting most reliable eigenmodes up to a predefined number perdownlink channel between an access point and every individual userterminal.

Certain embodiments provide a computer-program product for signaling ina multiuser wireless communication system with full feedback, comprisinga computer readable medium having instructions stored thereon, theinstructions being executable by one or more processors. Theinstructions generally include instructions for estimating a channelbetween an access point and a user terminal based on a received trainingsequence, and instructions for transmitting a quantized version of anormalized full downlink channel matrix and a quantized version ofestimated channel quality information (CQI).

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above-recited features of the presentdisclosure can be understood in detail, a more particular description,briefly summarized above, may be had by reference to embodiments, someof which are illustrated in the appended drawings. It is to be noted,however, that the appended drawings illustrate only certain typicalembodiments of this disclosure and are therefore not to be consideredlimiting of its scope, for the description may admit to other equallyeffective embodiments.

FIG. 1 shows a multiple-input multiple-output (MIMO) system with oneaccess point and a plurality of multi-antenna user terminals inaccordance with certain embodiments of the present disclosure.

FIG. 2 shows a block diagram of an access point and a plurality of userterminals in accordance with certain embodiments of the presentdisclosure.

FIG. 3 illustrates various components that may be utilized in a wirelessdevice in accordance with certain embodiments of the present disclosure.

FIG. 4 shows example operations for communicating between the accesspoint and user terminals with explicit compact feedback in an effort togenerate a preceding matrix at the access point, in accordance withcertain embodiments of the present disclosure.

FIG. 4A illustrates example components capable of performing theoperations illustrated in FIG. 4.

FIG. 5 shows example operations for communicating between the accesspoint and user terminals with implicit (hybrid) feedback in an effort togenerate a preceding matrix at the access point, in accordance withcertain embodiments of the present disclosure.

FIG. 5A illustrates example components capable of performing theoperations illustrated in FIG. 5.

FIG. 6 shows example operations for communicating between the accesspoint and user terminals with explicit full feedback in an effort togenerate a preceding matrix at the access point, in accordance withcertain embodiments of the present disclosure.

FIG. 6A illustrates example components capable of performing theoperations illustrated in FIG. 6.

DETAILED DESCRIPTION

The word “exemplary” is used herein to mean “serving as an example,instance, or illustration.” Any embodiment described herein as“exemplary” is not necessarily to be construed as preferred oradvantageous over other embodiments.

An Example Wireless Communication System

The techniques described herein may be used for various broadbandwireless communication systems, including communication systems that arebased on an orthogonal multiplexing scheme. Examples of suchcommunication systems include Orthogonal Frequency Division MultipleAccess (OFDMA) systems, Single-Carrier Frequency Division MultipleAccess (SC-FDMA) systems, and so forth. An OFDMA system utilizesorthogonal frequency division multiplexing (OFDM), which is a modulationtechnique that partitions the overall system bandwidth into multipleorthogonal sub-carriers. These sub-carriers may also be called tones,bins, etc. With OFDM, each sub-carrier may be independently modulatedwith data. An SC-FDMA system may utilize interleaved FDMA (IFDMA) totransmit on sub-carriers that are distributed across the systembandwidth, localized FDMA (LFDMA) to transmit on a block of adjacentsub-carriers, or enhanced FDMA (EFDMA) to transmit on multiple blocks ofadjacent sub-carriers. In general, modulation symbols are sent in thefrequency domain with OFDM and in the time domain with SC-FDMA.

One specific example of a communication system based on an orthogonalmultiplexing scheme is a WiMAX system. WiMAX, which stands for theWorldwide Interoperability for Microwave Access, is a standards-basedbroadband wireless technology that provides high-throughput broadbandconnections over long distances. There are two main applications ofWiMAX today: fixed WiMAX and mobile WiMAX. Fixed WiMAX applications arepoint-to-multipoint, enabling broadband access to homes and businesses,for example. Mobile WiMAX offers the full mobility of cellular networksat broadband speeds.

IEEE 802.16x is an emerging standard organization to define an airinterface for fixed and mobile broadband wireless access (BWA) systems.IEEE 802.16x approved “IEEE P802.16d/D5-2004” in May 2004 for fixed BWAsystems and published “IEEE P802.16e/D12 October 2005” in October 2005for mobile BWA systems. Those two standards defined four differentphysical layers (PHYs) and one media access control (MAC) layer. TheOFDM and OFDMA physical layer of the four physical layers are the mostpopular in the fixed and mobile BWA areas respectively.

FIG. 1 shows a multiple-access MIMO system 100 with access points anduser terminals. For simplicity, only one access point 110 is shown inFIG. 1. An access point is generally a fixed station that communicateswith the user terminals and may also be referred to as a base station orsome other terminology. A user terminal may be fixed or mobile and mayalso be referred to as a mobile station, a wireless device or some otherterminology. Access point 110 may communicate with one or more userterminals 120 at any given moment on the downlink and uplink. Thedownlink (i.e., forward link) is the communication link from the accesspoint to the user terminals, and the uplink (i.e., reverse link) is thecommunication link from the user terminals to the access point. A userterminal may also communicate peer-to-peer with another user terminal. Asystem controller 130 couples to and provides coordination and controlfor the access points.

While portions of the following disclosure will describe user terminals120 capable of communicating via SDMA, for certain embodiments, the userterminals 120 may also include some user terminals that do not supportSDMA. Thus, for such embodiments, an AP 110 may be configured tocommunicate with both SDMA and non-SDMA user terminals. This approachmay conveniently allow older versions of user terminals (“legacy”stations) to remain deployed in an enterprise, extending their usefullifetime, while allowing newer SDMA user terminals to be introduced asdeemed appropriate.

System 100 employs multiple transmit and multiple receive antennas fordata transmission on the downlink and uplink. Access point 110 isequipped with N_(ap) antennas and represents the multiple-input (MI) fordownlink transmissions and the multiple-output (MO) for uplinktransmissions. A set of K selected user terminals 120 collectivelyrepresents the multiple-output for downlink transmissions and themultiple-input for uplink transmissions. For pure SDMA, it is desired tohave N_(ap)≧K≧1 if the data symbol streams for the K user terminals arenot multiplexed in code, frequency or time by some means. K may begreater than N_(ap) if the data symbol streams can be multiplexed usingdifferent code channels with CDMA, disjoint sets of subbands with OFDM,and so on. Each selected user terminal transmits user-specific data toand/or receives user-specific data from the access point. In general,each selected user terminal may be equipped with one or multipleantennas (i.e., N_(ut)≧1). The K selected user terminals can have thesame or different number of antennas.

The SDMA system 100 may be a time division duplex (TDD) system or afrequency division duplex (FDD) system. For a TDD system, the downlinkand uplink share the same frequency band. For an FDD system, thedownlink and uplink use different frequency bands. MIMO system 100 mayalso utilize a single carrier or multiple carriers for transmission.Each user terminal may be equipped with a single antenna (e.g., in orderto keep costs down) or multiple antennas (e.g., where the additionalcost can be supported).

FIG. 2 shows a block diagram of access point 110 and two user terminals120 m and 120 x in MIMO system 100. Access point 110 is equipped with N.antennas 224 a through 224 t. User terminal 120 m is equipped withN_(ut,m) antennas 252 ma through 252 mu, and user terminal 120 x isequipped with N_(ut,x) antennas 252 xa through 252 xu. Access point 110is a transmitting entity for the downlink and a receiving entity for theuplink. Each user terminal 120 is a transmitting entity for the uplinkand a receiving entity for the downlink. As used herein, a “transmittingentity” is an independently operated apparatus or device capable oftransmitting data via a wireless channel, and a “receiving entity” is anindependently operated apparatus or device capable of receiving data viaa wireless channel. In the following description, the subscript “dn”denotes the downlink, the subscript “up” denotes the uplink, N_(up) userterminals are selected for simultaneous transmission on the uplink,N_(dn) user terminals are selected for simultaneous transmission on thedownlink, N_(up) may or may not be equal to N_(dn), and N_(up) andN_(dn) may be static values or can change for each scheduling interval.The beam-steering or some other spatial processing technique may be usedat the access point and user terminal.

In the uplink, at each user terminal 120 selected for uplinktransmission, a TX data processor 288 receives traffic data from a datasource 286 and control data from a controller 280. TX data processor 288processes (e.g., encodes, interleaves, and modulates) the traffic datafor the user terminal based on the coding and modulation schemesassociated with the rate selected for the user terminal and provides adata symbol stream. A TX spatial processor 290 performs spatialprocessing on the data symbol stream and provides N_(ut,m) transmitsymbol streams for the N_(ut,m) antennas. Each transmitter unit (TMTR)254 receives and processes (e.g., converts to analog, amplifies,filters, and frequency upconverts) a respective transmit symbol streamto generate an uplink signal. N_(ut,m) transmitter units 254 provideN_(ut,m) uplink signals for transmission from N_(ut,m) antennas 252 tothe access point.

N_(up) user terminals may be scheduled for simultaneous transmission onthe uplink. Each of these user terminals performs spatial processing onits data symbol stream and transmits its set of transmit symbol streamson the uplink to the access point.

At access point 110, N_(ap) antennas 224 a through 224 ap receive theuplink signals from all N_(up) user terminals transmitting on theuplink. Each antenna 224 provides a received signal to a respectivereceiver unit (RCVR) 222. Each receiver unit 222 performs processingcomplementary to that performed by transmitter unit 254 and provides areceived symbol stream. An RX spatial processor 240 performs receiverspatial processing on the N_(ap) received symbol streams from N_(ap)receiver units 222 and provides N_(up) recovered uplink data symbolstreams. The receiver spatial processing is performed in accordance withthe channel correlation matrix inversion (CCMI), minimum mean squareerror (MMSE), soft interference cancellation (SIC), or some othertechnique. Each recovered uplink data symbol stream is an estimate of adata symbol stream transmitted by a respective user terminal. An RX dataprocessor 242 processes (e.g., demodulates, deinterleaves, and decodes)each recovered uplink data symbol stream in accordance with the rateused for that stream to obtain decoded data. The decoded data for eachuser terminal may be provided to a data sink 244 for storage and/or acontroller 230 for further processing.

In the downlink, at access point 110, a TX data processor 210 receivestraffic data from a data source 208 for N_(dn) user terminals scheduledfor downlink transmission, control data from a controller 230, andpossibly other data from a scheduler 234. The various types of data maybe sent on different transport channels. TX data processor 210 processes(e.g., encodes, interleaves, and modulates) the traffic data for eachuser terminal based on the rate selected for that user terminal. TX dataprocessor 210 provides N_(dn) downlink data symbol streams for theN_(dn) user terminals. A TX spatial processor 220 performs spatialprocessing (such as a precoding or beamforming, as described in thepresent disclosure) on the N_(dn) downlink data symbol streams, andprovides N_(ap) transmit symbol streams for the N_(ap) antennas. Eachtransmitter unit 222 receives and processes a respective transmit symbolstream to generate a downlink signal. N_(ap) transmitter units 222providing N_(ap) downlink signals for transmission from N_(ap) antennas224 to the user terminals.

At each user terminal 120, N_(ut,m) antennas 252 receive the N_(ap)downlink signals from access point 110. Each receiver unit 254 processesa received signal from an associated antenna 252 and provides a receivedsymbol stream. An RX spatial processor 260 performs receiver spatialprocessing on N_(ut,m) received symbol streams from N_(ut,m) receiverunits 254 and provides a recovered downlink data symbol stream for theuser terminal. The receiver spatial processing is performed inaccordance with the CCMI, MMSE or some other technique. An RX dataprocessor 270 processes (e.g., demodulates, deinterleaves and decodes)the recovered downlink data symbol stream to obtain decoded data for theuser terminal.

At each user terminal 120, a channel estimator 278 estimates thedownlink channel response and provides downlink channel estimates, whichmay include channel gain estimates, SNR estimates, noise variance and soon. Similarly, a channel estimator 228 estimates the uplink channelresponse and provides uplink channel estimates. Controller 280 for eachuser terminal typically derives the spatial filter matrix for the userterminal based on the downlink channel response matrix H_(dn,m) for thatuser terminal. Controller 230 derives the spatial filter matrix for theaccess point based on the effective uplink channel response matrixH_(u,eff). Controller 280 for each user terminal may send feedbackinformation (e.g., the downlink and/or uplink eigenvectors, eigenvalues,SNR estimates, and so on) to the access point. Controllers 230 and 280also control the operation of various processing units at access point110 and user terminal 120, respectively.

FIG. 3 illustrates various components that may be utilized in a wirelessdevice 302 that may be employed within the wireless communication system100. The wireless device 302 is an example of a device that may beconfigured to implement the various methods described herein. Thewireless device 302 may be a base station 104 or a user terminal 106.

The wireless device 302 may include a processor 304 which controlsoperation of the wireless device 302. The processor 304 may also bereferred to as a central processing unit (CPU). Memory 306, which mayinclude both read-only memory (ROM) and random access memory (RAM),provides instructions and data to the processor 304. A portion of thememory 306 may also include non-volatile random access memory (NVRAM).The processor 304 typically performs logical and arithmetic operationsbased on program instructions stored within the memory 306. Theinstructions in the memory 306 may be executable to implement themethods described herein.

The wireless device 302 may also include a housing 308 that may includea transmitter 310 and a receiver 312 to allow transmission and receptionof data between the wireless device 302 and a remote location. Thetransmitter 310 and receiver 312 may be combined into a transceiver 314.A single or a plurality of transmit antennas 316 may be attached to thehousing 308 and electrically coupled to the transceiver 314. Thewireless device 302 may also include (not shown) multiple transmitters,multiple receivers, and multiple transceivers.

The wireless device 302 may also include a signal detector 318 that maybe used in an effort to detect and quantify the level of signalsreceived by the transceiver 314. The signal detector 318 may detect suchsignals as total energy, energy per subcarrier per symbol, powerspectral density and other signals. The wireless device 302 may alsoinclude a digital signal processor (DSP) 320 for use in processingsignals.

The various components of the wireless device 302 may be coupledtogether by a bus system 322, which may include a power bus, a controlsignal bus, and a status signal bus in addition to a data bus.

The wireless system shown in FIGS. 1-3 may refer to the SDMA systemwhere antennas at the access point are located in sufficiently differentdirections, which insures no interference between simultaneouslytransmitted spatial streams dedicated to different user terminals. Forcertain embodiments of the present disclosure, the wireless system shownin FIGS. 1-3 may refer to the multiuser system where a preceding(beamforming) of the transmission signal is applied providingorthogonality between spatial streams dedicated to different userterminals, while the access point antennas do not necessarily need to belocated in sufficiently different directions.

Multiuser Mimo System Model

As shown in FIG. 1, user terminals 120 may be distributed throughout thecoverage area of the access point 110. The access point 110 may beequipped with multiple (N_(ap)=N_(y)) antennas for data transmission.Every user terminal 120 may be equipped with multiple antennas for datareception. User terminals in the system may be equipped with the same ordifferent numbers of antennas. For simplicity and without losinggenerality, it can be assumed that all user terminals 120 in themultiuser MIMO system 100 may be equipped with the same number ofantennas (N_(ut)=N_(r)).

In general, different MIMO channels are formed by the N_(t) antennas atthe access point and the N_(r) antennas at each user terminal. For asingle-carrier MIMO system, a MIMO channel formed by the N, antennas atthe access point and the N_(r) antennas at a given k^(th) user terminal(k=1, . . . , K, where K is a total number of user terminals in themultiuser system 100) can be characterized by an N_(r)×N_(t) channelresponse matrix H_(k), which may be expressed as:

$\begin{matrix}{{H_{k} = \begin{bmatrix}h_{1,1}^{k} & h_{1,2}^{k} & \ldots & h_{1,N_{t}}^{k} \\h_{2,1}^{k} & h_{2,2}^{k} & \ldots & h_{2,N_{t}}^{k} \\\vdots & \vdots & \ddots & \vdots \\h_{N_{r},1}^{k} & h_{N_{r},2}^{k} & \ldots & h_{N_{r},N_{t}}^{k}\end{bmatrix}},} & (1)\end{matrix}$where entry h_(i,j) ^(k), for i=1, . . . , N_(r) and j=1, . . . , N_(t),denotes the coupling or complex gain between the access point antenna jand antenna i of the k^(th) user terminal.

Data may be transmitted in various manners in the multiuser wirelesssystem. For certain embodiments of the present disclosure, N_(S)modulated data symbol streams may be mapped to N_(t) transmit antennasusing a proposed preceding technique. Therefore, N_(S) modulated symbolstreams may be transmitted simultaneously from the N_(t) antennas at theaccess point. The N_(S) _(k) spatial data streams out of N_(S) may bededicated to the k^(th) user terminal, where N_(S) _(k) ≦N_(S) and

${{\sum\limits_{k = 1}^{K}N_{S_{k}}} = N_{S}},{{{for}\mspace{14mu} k} = 1},\ldots\;,{K.}$

The received symbols at the k^(th) user terminal for this transmissionscheme may be expressed as:y _(k) =H _(k) x+n _(k),  (2)where x is a post-precoding N_(t)×1 vector of complex numbers to betransmitted by the access point, y_(k) is an N_(r)×1 vector with entriesfor N_(r) received symbols obtained via the N_(r) antennas at the k^(th)user terminal, and n_(k) is a noise vector observed at the k^(th) userterminal. For simplicity, the noise may be assumed to be additive whiteGaussian noise (AWGN) with a zero mean vector and a covariance matrix ofΛ_(k)=σ_(k) ²I, where σ_(k) ² is a variance of the noise observed by thek^(th) user terminal and I is the identity matrix.

The preceding technique applied at the transmitter may provideorthogonality between users. Therefore, there may be no inter-userinterference between separate N_(S) _(k) spatial streams dedicated forthe arbitrary user terminal k, where k=1, . . . , K. However, datasymbol streams transmitted from the N_(t) antennas at the access pointmay interfere with each other at the k^(th) user terminal. A given datasymbol stream transmitted from one access point antenna may be receivedby all N_(r) user terminal antennas at different amplitudes and phases.Each received symbol stream includes a component of each of the N_(S)_(k) data symbol streams dedicated to the k^(th) user terminal. TheN_(r) received symbol streams would collectively include all of theN_(S) _(k) data symbol streams. However, these N_(S) _(k) data symbolstreams may be dispersed among the N_(r) received symbol streams. Thek^(th) user terminal may perform receiver spatial processing on theN_(r) received symbol streams to recover the N_(S) _(k) data symbolstreams dedicated to the k^(th) user terminal.

The achievable performance for the arbitrary k^(th) user terminal may bedependent (to a large extent) on its channel response matrix H_(k). If ahigh degree of correlation exists within H_(k), then each data symbolstream out of N_(S) _(k) spatial streams would observe a large amount ofinterference from other streams dedicated to the k^(th) user terminal,which cannot be sufficiently removed by the receiver spatial processingat the user terminal. The high level of interference degrades the SNR ofeach affected data symbol stream, possibly to a point where the datasymbol stream cannot be decoded correctly by the user terminal. In thepresent disclosure, a linear precoding based on eigenmode selection anda minimum mean square error technique (hereinafter abbreviated as theMMSE-ES) is proposed that decreases correlation between differentspatial streams dedicated to the same user terminal and increasestransmission capacity, while providing orthogonality between distinctuser terminals.

MMSE Linear Precoding in Multiuser MIMO System

Once the channel matrix H_(k) from equation (2) is estimated at thearbitrary k^(th) user terminal that also includes the squaredpath-losses for modulated spatial streams dedicated to that userterminal, the singular-value decomposition of the matrix H_(k) may beperformed at every user terminal as:H _(k) =U _(k) ·S _(k) ·V _(k) ^(H) ,k=1, . . . , K,  (3)where U_(k) is an N_(r)×N_(r) matrix of left eigenvectors, S_(k) is anN_(r)×N_(r) diagonal matrix of eigenvalues for N_(r) spatial streams,and V_(k) is an N_(t)×N_(r) matrix of right eigenvectors. It can beassumed, without losing generality, that each user terminal k (k=1, . .. , K) may select N_(S) _(k) dominant eigenmodes and feed back relatedinformation about selected eigenmodes, such as the quantizedeigenvectors and eigenvalues, to the access point.

When the access point obtains through feedback the quantizedeigenvectors and related eigenvalues of all K MIMO channels in thesystem (i.e., from all K user terminals), an equivalent channel matrixbased on selected N_(S) _(k) eigenmodes per user terminal k (k=1, . . ., K) may be generated at the access point as:{tilde over (H)}=[V ₁(:,1:N _(S) ₁ )·S ₁(1:N _(S) ₁ :N _(S) ₁ ), . . . ,V _(K)(:,1:N _(S) _(K) )·S _(K)(1:N _(S) _(K) ,1:N _(S) _(K))]^(H).  (4)

The general per-tone MMSE-ES preceding may be represented as (tone indexcan be omitted for simplicity):W=└{tilde over (H)} ^(H)Ψ^(1/2)·(Σ²+Ψ^(1/2) {tilde over (H)}{tilde over(H)} ^(H)Ψ^(2/2))⁻¹┘·Φ,  (5)W= W·Q ^(1/2),  (6)where W is a preceding matrix, Ψ, Φ and Q are diagonal matrices thatdefine the preceding filter depending on a specific optimizationobjective, Σ²=diag(Σ₁ ², . . . , Σ_(K) ²) while Σ_(k) ²=σ_(k) ²I_(N)_(Sk) , and σ_(k) ² is a variance of the noise observed by the k^(th)user terminal.

The presented formulation is general and allows for differentoptimizations.

The N_(S) modulated symbols may be preprocessed with the precedingmatrix W given by equation (6) to obtain N_(t) spatially processed,beamformed symbols that may be simultaneously transmitted to all userterminals on the most reliable eigenmodes of every MIMO channel betweenthe access point and every individual user terminal. The spatialprocessing (i.e. beamforming) using the computed precoding matrix may begiven as:x=W·s,  (7)where s is an N_(S)×1 vector of modulated transmission symbols, and x isthe N_(t)×1 vector from equation (2) of spatially processed modulatedsymbols that may be simultaneously transmitted to the K distinct userterminals and represents a linear combination of the users' datasignals.

After the preprocessing given by equation (7) is performed, the spatialstreams that are dedicated to different users may be mutuallyorthogonal. Therefore, there may be no inter-user interference oftransmitted spatial streams from the access point to the K userterminals. In addition, the MMSE precoding technique applied at theaccess point may decrease a level of correlation within the MIMO channelmatrix given by equation (1) (i.e., a level of correlation betweendifferent spatial streams dedicated to the same user terminal).Therefore, in order to achieve the same SNR level per user terminal aspreceding techniques from the prior art, smaller transmission power maybe implicated if the proposed MMSE preceding scheme is applied at theaccess point. Consequently, for the same transmission power the MMSEpreceding scheme may provide increased transmission capacity per userterminal compared to preceding techniques from the prior art.

Signaling Between Access Point and User Terminals for GeneratingPrecoding Matrix

FIG. 4 shows example operations for communicating between the accesspoint and user terminals with explicit (compact) feedback for generatinga preceding matrix at the access point. At the beginning of theoperations, at 410, the access point may send to every user terminal inthe system a predefined training sequence indicating the maximum numberof spatial streams for which every user terminal can send feedback. At420, each user terminal may estimate a MIMO channel between the accesspoint and the corresponding user terminal based on the received trainingsequence. Subsequently, at 430, each user terminal may perform thesingular value decomposition (SVD), compute eigenvalues and eigenvectorsof the estimated channel, as given by equation (3), and select up to thespecified number of the most reliable eigenmodes that correspond to thelargest eigenvalues to be fed back to the access point.

At 440, the access point may receive (via feedback channels from everyuser terminal) a quantized version of selected eigenvectors, relatedquantized eigenvalues, and the quantized channel quality information(CQI), such as the information about the estimatedsignal-to-interference-plus-noise ratio (SINR) or noise variance atevery user terminal. At 450, the access point may compute the precedingmatrix based on the received eigenvectors, corresponding eigenvalues,and the CQI according to the MMSE technique, as given by equations(5)-(6).

At 460, the access point may start an SDMA transmission by sending asingle spatial stream per user terminal that carries informationregarding the number of spatial streams allocated to that particularuser terminal. At 470, the access point may preprocess data and thepreceding training sequence using the preceding matrix, as given byequation (7). At 480, the access point may transmit the precoded data onthe selected most reliable eigenmodes that are preceded by the precodedtraining sequence. At 490, every user terminal may receive the precodedsignal (including the precoded data and precoded training sequence) fromthe access point, estimate the precoded channel gain using the precodedtraining sequence, and apply a spatial filter to the received precodeddata to recover the specified number of spatial streams dedicated toeach individual user terminal.

FIG. 5 shows example operations for communicating between the accesspoint and user terminals with implicit (hybrid) feedback in an effort togenerate a preceding matrix at the access point. At 510, every userterminal may send to the access point a sounding sequence along withexplicit data carrying the quantized version of the estimated SINR ateach particular user terminal. At 520, the access point may estimatefull uplink channels based on received sounding sequences from all userterminals. At 530, the access point may estimate MIMO downlink channelsbetween the access point and each individual user terminal assumingreciprocity of corresponding uplink and downlink MIMO channels.

At 540, the access point may compute eigenvalues and eigenvectors of theestimated downlink channels as given by equation (3), and the accesspoint may then select the most reliable eigenmodes up to the predefinednumber N_(S) _(k) per MIMO downlink channel that corresponds to thek^(th) user terminal, k=1, . . . , K, where

${\sum\limits_{k = 1}^{K}N_{S_{k}}} = {N_{S}.}$At 550, using the computed eigenvectors, related eigenvalues, andestimated SINR, the access point may generate the preceding matrix Wbased on the MMSE technique, as given by equations (5)-(6).

At 560, the access point may start the SDMA transmission by sending asingle spatial stream per user terminal that carries informationregarding the number of spatial streams allocated to the user terminal.At 570, the access point may preprocess data and the preceding trainingsequence using the preceding matrix, as given by equation (7). At 580,the access point may transmit the precoded data on the selected mostreliable eigenmodes preceded by the precoded training sequence. At 590,every user terminal may receive the precoded signal (including theprecoded data and precoded training sequence) from the access point,estimate the precoded channel gain using the precoded training sequence,and apply a spatial filter to the received precoded data to recover thespecified number of spatial streams dedicated to each individual userterminal.

FIG. 6 shows example operations for communicating between the accesspoint and user terminals with explicit full feedback between userterminals and the access point in an effort to generate a precedingmatrix at the access point. At 610, the access point may send to everyuser terminal a predefined training sequence. Subsequently, at 620,every user terminal may estimate the MIMO downlink channel between theaccess point and the corresponding user terminal using the receivedtraining sequence. At 630, each user terminal may send back to theaccess point a quantized version of the normalized full downlink channelmatrix and a quantized version of the estimated SINR at every userterminal.

At 640, the access point may compute eigenvalues and eigenvectors of theestimated downlink channels as given by equation (3), and the accesspoint may then select the most reliable eigenmodes up to the predefinednumber N_(S) _(k) per MIMO downlink channel that corresponds to thek^(th) user terminal, k=1, . . . , K, where

${\sum\limits_{k = 1}^{K}N_{S_{k}}} = {N_{S}.}$At 650, using the computed eigenvectors, related eigenvalues, andestimated SINR, the access point may generate the preceding matrix Wbased on the MMSE technique, as given by equations (5)-(6).

At 660, the access point may start the SDMA transmission by sending asingle spatial stream per user terminal that carries informationregarding the number of spatial streams allocated to the user terminal.At 670, the access point may preprocess data and the preceding trainingsequence using the preceding matrix, as given by equation (7). At 680,the access point may transmit the precoded data on the selected mostreliable eigenmodes preceded by the precoded training sequence. At 690,every user terminal may receive the precoded signal from the accesspoint, estimate the precoded channel gain using the precoded trainingsequence, and apply a spatial filter to the received precoded data torecover the specified number of spatial streams dedicated to eachindividual user terminal.

The various operations of methods described above may be performed byvarious hardware and/or software component(s) and/or module(s)corresponding to means-plus-function blocks illustrated in the Figures.For example, blocks 410-490 illustrated in FIG. 4 correspond tomeans-plus-function blocks 410A-490A illustrated in FIG. 4A. Similarly,blocks 510-590 illustrated in FIG. 5 correspond to means-plus-functionblocks 510A-590A illustrated in FIG. 5A. Similarly, blocks 610-690illustrated in FIG. 6 correspond to means-plus-function blocks 610A-690Aillustrated in FIG. 6A. More generally, where there are methodsillustrated in Figures having corresponding counterpartmeans-plus-function Figures, the operation blocks correspond tomeans-plus-function blocks with similar numbering.

The various illustrative logical blocks, modules and circuits describedin connection with the present disclosure may be implemented orperformed with a general purpose processor, a digital signal processor(DSP), an application specific integrated circuit (ASIC), a fieldprogrammable gate array signal (FPGA) or other programmable logic device(PLD), discrete gate or transistor logic, discrete hardware componentsor any combination thereof designed to perform the functions describedherein. A general purpose processor may be a microprocessor, but in thealternative, the processor may be any commercially available processor,controller, microcontroller or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

The steps of a method or algorithm described in connection with thepresent disclosure may be embodied directly in hardware, in a softwaremodule executed by a processor, or in a combination of the two. Asoftware module may reside in any form of storage medium that is knownin the art. Some examples of storage media that may be used includerandom access memory (RAM), read only memory (ROM), flash memory, EPROMmemory, EEPROM memory, registers, a hard disk, a removable disk, aCD-ROM and so forth. A software module may comprise a singleinstruction, or many instructions, and may be distributed over severaldifferent code segments, among different programs, and across multiplestorage media. A storage medium may be coupled to a processor such thatthe processor can read information from, and write information to, thestorage medium. In the alternative, the storage medium may be integralto the processor.

The methods disclosed herein comprise one or more steps or actions forachieving the described method. The method steps and/or actions may beinterchanged with one another without departing from the scope of theclaims. In other words, unless a specific order of steps or actions isspecified, the order and/or use of specific steps and/or actions may bemodified without departing from the scope of the claims.

The functions described may be implemented in hardware, software,firmware or any combination thereof. If implemented in software, thefunctions may be stored as one or more instructions on acomputer-readable medium. A storage media may be any available mediathat can be accessed by a computer. By way of example, and notlimitation, such computer-readable media can comprise RAM, ROM, EEPROM,CD-ROM or other optical disk storage, magnetic disk storage or othermagnetic storage devices, or any other medium that can be used to carryor store desired program code in the form of instructions or datastructures and that can be accessed by a computer. Disk and disc, asused herein, include compact disc (CD), laser disc, optical disc,digital versatile disc (DVD), floppy disk, and Blu-ray® disc where disksusually reproduce data magnetically, while discs reproduce dataoptically with lasers.

Software or instructions may also be transmitted over a transmissionmedium. For example, if the software is transmitted from a website,server, or other remote source using a coaxial cable, fiber optic cable,twisted pair, digital subscriber line (DSL), or wireless technologiessuch as infrared, radio, and microwave, then the coaxial cable, fiberoptic cable, twisted pair, DSL, or wireless technologies such asinfrared, radio, and microwave are included in the definition oftransmission medium.

Further, it should be appreciated that modules and/or other appropriatemeans for performing the methods and techniques described herein can bedownloaded and/or otherwise obtained by a user terminal and/or basestation as applicable. For example, such a device can be coupled to aserver to facilitate the transfer of means for performing the methodsdescribed herein. Alternatively, various methods described herein can beprovided via storage means (e.g., RAM, ROM, a physical storage mediumsuch as a compact disc (CD) or floppy disk, etc.), such that a userterminal and/or base station can obtain the various methods uponcoupling or providing the storage means to the device. Moreover, anyother suitable technique for providing the methods and techniquesdescribed herein to a device can be utilized.

It is to be understood that the claims are not limited to the preciseconfiguration and components illustrated above. Various modifications,changes and variations may be made in the arrangement, operation anddetails of the methods and apparatus described above without departingfrom the scope of the claims.

1. A method for signaling in a multiuser wireless communication systemwith compact feedback, comprising: sending to a plurality of userterminals a predefined training sequence indicating a maximum number ofspatial streams for each of the user terminals to send feedback;receiving via feedback channels from each of the user terminals aquantized version of selected eigenvectors, corresponding quantizedeigenvalues, and quantized channel quality information (CQI); computinga precoding matrix based on the received eigenvectors, the correspondingeigenvalues, and the CQI; sending a single spatial stream per userterminal that carries information regarding a number of spatial streamsallocated to that specific user terminal; performing preprocessing ofdata and of a preceding training sequence using the computed precodingmatrix; and transmitting precoded data preceded by the precoded trainingsequence along with an indication of the number of spatial streams to beprocessed at every user terminal.
 2. The method of claim 1, wherein theprecoding matrix is computed according to a minimum mean square error(MMSE) technique.
 3. The method of claim 1, wherein the CQI comprises asignal-to-interference-plus-noise ratio (SINR) at each of the userterminals.
 4. A method for signaling in a multiuser wirelesscommunication system with hybrid feedback, comprising: estimating fulluplink channels based on a sounding sequences received from a pluralityof user terminals; estimating a downlink channel between the accesspoint and each of the user terminals assuming reciprocity ofcorresponding uplink and downlink channels; computing eigenvalues andeigenvectors of estimated downlink channels; selecting most reliableeigenmodes up to a predefined number per downlink channel between theaccess point and each of the user terminals; generating a precodingmatrix based on computed selected eigenvectors, correspondingeigenvalues, and estimated channel quality information (CQI); sending asingle spatial stream per user terminal that carries informationregarding the number of spatial streams allocated to that specific userterminal; performing preprocessing of data and of a preceding trainingsequence using the precoding matrix; and transmitting the precoded datapreceded by the precoded training sequence along with an indication ofthe number of spatial streams to be processed at every user terminal. 5.The method of claim 4, wherein the precoding matrix is generated using aminimum mean square error (MMSE) technique.
 6. The method of claim 4,wherein the CQI comprises a signal-to-interference-plus-noise ratio(SINR) at every user terminal.
 7. A method for signaling in a multiuserwireless communication system with full feedback, comprising:transmitting a predefined training sequence; computing eigenvalues andeigenvectors of estimated downlink channels; selecting most reliableeigenmodes up to a predefined number per downlink channel between anaccess point and every individual user terminal; generating a precodingmatrix based on computed selected eigenvectors, correspondingeigenvalues, and estimated channel quality information (CQI); sending asingle spatial stream per user terminal that carries informationregarding the number of spatial streams allocated to that specific userterminal; performing preprocessing of data and of a preceding trainingsequence using the precoding matrix; and transmitting precoded datapreceded by a precoded training sequence along with an indication of thenumber of spatial streams to be processed at every user terminal.
 8. Themethod of claim 7, wherein the precoding matrix is generated using aminimum mean square error (MMSE) technique.
 9. The method of claim 7,wherein the CQI comprises a signal-to-interference-plus-noise ratio(SINR) at every user terminal.
 10. A method for signaling in a multiuserwireless communication system with full feedback, comprising: estimatinga channel between an access point and a user terminal based on areceived training sequence; transmitting a quantized version of anormalized full downlink channel matrix and a quantized version ofestimated channel quality information (CQI); receiving a precodedtraining sequence; estimating a precoded channel gain using the precodedtraining sequence; and applying a spatial filter to received precodeddata to recover a specified number of spatial streams dedicated to theuser terminal.
 11. The method of claim 10, wherein the CQI comprises asignal-to-interference-plus-noise ratio (SINR) at the user terminal. 12.An apparatus for signaling in a multiuser wireless communication systemwith compact feedback, comprising: logic for sending to a plurality ofuser terminals a predefined training sequence indicating a maximumnumber of spatial streams for each of the user terminals to sendfeedback; and logic for receiving via feedback channels from each of theuser terminals a quantized version of selected eigenvectors,corresponding quantized eigenvalues, and quantized channel qualityinformation (CQI); logic for computing a precoding matrix based on thereceived eigenvectors, the corresponding eigenvalues, and the CQI; logicfor sending a single spatial stream per user terminal that carriesinformation regarding a number of spatial streams allocated to thatspecific user terminal; logic for performing preprocessing of data andof a preceding training sequence using the computed precoding matrix;and logic for transmitting precoded data preceded by the precodedtraining sequence along with an indication of the number of spatialstreams to be processed at every user terminal.
 13. The apparatus ofclaim 12, wherein the precoding matrix is computed according to aminimum mean square error (MMSE) technique.
 14. The apparatus of claim12, wherein the CQI comprises a signal-to-interference-plus-noise ratio(SINR) at each of the user terminals.
 15. An apparatus for signaling ina multiuser wireless communication system with compact feedback,comprising: logic for estimating a channel between an access point and auser terminal based on a received training sequence; logic forperforming a singular value decomposition to compute eigenvalues andeigenvectors of the estimated channel; logic for selecting up to aspecified number of most reliable eigenmodes to be fed back to theaccess point; logic for receiving a precoded signal comprising precodeddata and a precoded training sequence; logic for estimating the precodedchannel gain using the precoded training sequence; and logic forapplying a spatial filter to the received precoded data to recover aspecified number of spatial streams dedicated to each individual userterminal.
 16. An apparatus for signaling in a multiuser wirelesscommunication system with hybrid feedback, comprising: logic forestimating full uplink channels based on a sounding sequences receivedfrom a plurality of user terminals; logic for estimating a downlinkchannel between the access point and each of the user terminals assumingreciprocity of corresponding uplink and downlink channels; logic forcomputing eigenvalues and eigenvectors of estimated downlink channels;and logic for selecting most reliable eigenmodes up to a predefinednumber per downlink channel between the access point and each of theuser terminals; logic for generating a precoding matrix based oncomputed selected eigenvectors, corresponding eigenvalues, and estimatedchannel quality information (CQI); logic for sending a single spatialstream per user terminal that carries information regarding the numberof spatial streams allocated to that specific user terminal; logic forperforming preprocessing of data and of a preceding training sequenceusing the precoding matrix; and logic for transmitting the precoded datapreceded by the precoded training sequence along with an indication ofthe number of spatial streams to be processed at every user terminal.17. The apparatus of claim 16, wherein the precoding matrix is generatedusing a minimum mean square error (MMSE) technique.
 18. The apparatus ofclaim 16, wherein the CQI comprises a signal-to-interference-plus-noiseratio (SINR) at every user terminal.
 19. An apparatus for signaling in amultiuser wireless communication system with hybrid feedback,comprising: logic for transmitting a sounding sequence along withexplicit data carrying a quantized version of estimated Channel QualityInformation (CQI) at a user terminal; logic for receiving a precodedsignal; logic for estimating a precoded channel gain using a precodedtraining sequence; and logic for applying a spatial filter to receivedprecoded data to recover a specified number of spatial streams dedicatedto the user terminal.
 20. The apparatus of claim 19, wherein the CQIcomprises a signal-to-interference-plus-noise ratio (SINR) at the userterminal.
 21. An apparatus for signaling in a multiuser wirelesscommunication system with full feedback, comprising: logic fortransmitting a predefined training sequence; logic for computingeigenvalues and eigenvectors of estimated downlink channels; logic forselecting most reliable eigenmodes up to a predefined number perdownlink channel between an access point and every individual userterminal; logic for generating a precoding matrix based on computedselected eigenvectors, corresponding eigenvalues, and estimated channelquality information (CQI); logic for sending a single spatial stream peruser terminal that carries information regarding the number of spatialstreams allocated to that specific user terminal; logic for performingpreprocessing of data and of a preceding training sequence using theprecoding matrix; and logic for transmitting precoded data preceded by aprecoded training sequence along with an indication of the number ofspatial streams to be processed at every user terminal.
 22. Theapparatus of claim 21, wherein the precoding matrix is generated using aminimum mean square error (MMSE) technique.
 23. The apparatus of claim21, wherein the CQI comprises a signal-to-interference-plus-noise ratio(SINR) at every user terminal.
 24. An apparatus for signaling in amultiuser wireless communication system with full feedback, comprising:logic for estimating a channel between an access point and a userterminal based on a received training sequence; logic for transmitting aquantized version of a normalized full downlink channel matrix and aquantized version of estimated channel quality information (CQI); logicfor receiving a precoded training sequence; logic for estimating aprecoded channel gain using the precoded training sequence; and logicfor applying a spatial filter to received precoded data to recover aspecified number of spatial streams dedicated to the user terminal. 25.The apparatus of claim 24, wherein the CQI comprises asignal-to-interference-plus-noise ratio (SINR) at the user terminal. 26.An apparatus for signaling in a multiuser wireless communication systemwith compact feedback, comprising: means for sending to a plurality ofuser terminals a predefined training sequence indicating a maximumnumber of spatial streams for each of the user terminals to sendfeedback; and means for receiving via feedback channels from each of theuser terminals a quantized version of selected eigenvectors,corresponding quantized eigenvalues, and quantized channel qualityinformation (CQI); means for computing a precoding matrix based on thereceived eigenvectors, the corresponding eigenvalues, and the CQI; meansfor sending a single spatial stream per user terminal that carriesinformation regarding a number of spatial streams allocated to thatspecific user terminal; means for performing preprocessing of data andof a preceding training sequence using the computed precoding matrix;and means for transmitting precoded data preceded by the precodedtraining sequence along with an indication of the number of spatialstreams to be processed at every user terminal.
 27. The apparatus ofclaim 26, wherein the precoding matrix is computed according to aminimum mean square error (MMSE) technique.
 28. The apparatus of claim26, wherein the CQI comprises a signal-to-interference-plus-noise ratio(SINR) at each of the user terminals.
 29. An apparatus for signaling ina multiuser wireless communication system with compact feedback,comprising: means for estimating a channel between an access point and auser terminal based on a received training sequence; means forperforming a singular value decomposition to compute eigenvalues andeigenvectors of the estimated channel; means for selecting up to aspecified number of most reliable eigenmodes to be fed back to theaccess point; means for receiving a precoded signal comprising precodeddata and a precoded training sequence; means for estimating the precodedchannel gain using the precoded training sequence; and means forapplying a spatial filter to the received precoded data to recover aspecified number of spatial streams dedicated to each individual userterminal.
 30. An apparatus for signaling in a multiuser wirelesscommunication system with hybrid feedback, comprising: means forestimating full uplink channels based on a sounding sequences receivedfrom a plurality of user terminals; means for estimating a downlinkchannel between the access point and each of the user terminals assumingreciprocity of corresponding uplink and downlink channels; means forcomputing eigenvalues and eigenvectors of estimated downlink channels;and means for selecting most reliable eigenmodes up to a predefinednumber per downlink channel between the access point and each of theuser terminals; means for generating a precoding matrix based oncomputed selected eigenvectors, corresponding eigenvalues, and estimatedchannel quality information (CQI); means for sending a single spatialstream per user terminal that carries information regarding the numberof spatial streams allocated to that specific user terminal; means forperforming preprocessing of data and of a preceding training sequenceusing the precoding matrix; and means for transmitting the precoded datapreceded by the precoded training sequence along with an indication ofthe number of spatial streams to be processed at every user terminal.31. The apparatus of claim 30, wherein the precoding matrix is generatedusing a minimum mean square error (MMSE) technique.
 32. The apparatus ofclaim 30, wherein the CQI comprises a signal-to-interference-plus-noiseratio (SINR) at every user terminal.
 33. An apparatus for signaling in amultiuser wireless communication system with hybrid feedback,comprising: means for transmitting a sounding sequence along withexplicit data carrying a quantized version of estimated Channel QualityInformation (CQI) at a user terminal; means for receiving a precodedsignal; means for estimating a precoded channel gain using a precodedtraining sequence; and means for applying a spatial filter to receivedprecoded data to recover a specified number of spatial streams dedicatedto the user terminal.
 34. The apparatus of claim 33, wherein the CQIcomprises a signal-to-interference-plus-noise ratio (SINR) at the userterminal.
 35. An apparatus for signaling in a multiuser wirelesscommunication system with full feedback, comprising: means fortransmitting a predefined training sequence; means for computingeigenvalues and eigenvectors of estimated downlink channels; and meansfor selecting most reliable eigenmodes up to a predefined number perdownlink channel between an access point and every individual userterminal means for generating a precoding matrix based on computedselected eigenvectors, corresponding eigenvalues, and estimated channelquality information (CQI); means for sending a single spatial stream peruser terminal that carries information regarding the number of spatialstreams allocated to that specific user terminal; means for performingpreprocessing of data and of a preceding training sequence using theprecoding matrix; and means for transmitting precoded data preceded by aprecoded training sequence along with an indication of the number ofspatial streams to be processed at every user terminal.
 36. Theapparatus of claim 35, wherein the precoding matrix is generated using aminimum mean square error (MMSE) technique.
 37. The apparatus of claim35, wherein the CQI comprises a signal-to-interference-plus-noise ratio(SINR) at every user terminal.
 38. An apparatus for signaling in amultiuser wireless communication system with full feedback, comprising:means for estimating a channel between an access point and a userterminal based on a received training sequence; means for transmitting aquantized version of a normalized full downlink channel matrix and aquantized version of estimated channel quality information (CQI); meansfor receiving a precoded training sequence; means for estimating aprecoded channel gain using the precoded training sequence; and meansfor applying a spatial filter to received precoded data to recover aspecified number of spatial streams dedicated to the user terminal. 39.The apparatus of claim 38, wherein the CQI comprises asignal-to-interference-plus-noise ratio (SINR) at the user terminal. 40.A non-transitory computer-program product for signaling in a multiuserwireless communication system with compact feedback, comprising acomputer readable medium having instructions stored thereon, theinstructions being executable by one or more processors and theinstructions comprising: instructions for sending to a plurality of userterminals a predefined training sequence indicating a maximum number ofspatial streams for each of the user terminals to send feedback; andinstructions for receiving via feedback channels from each of the userterminals a quantized version of selected eigenvectors, correspondingquantized eigenvalues, and quantized channel quality information (CQI);instructions for computing a precoding matrix based on the receivedeigenvectors, the corresponding eigenvalues, and the CQI; instructionsfor sending a single spatial stream per user terminal that carriesinformation regarding a number of spatial streams allocated to thatspecific user terminal; instructions for performing preprocessing ofdata and of a preceding training sequence using the computed precodingmatrix; and instructions for transmitting precoded data preceded by theprecoded training sequence along with an indication of the number ofspatial streams to be processed at every user terminal.
 41. Thenon-transitory computer-program product of claim 40, wherein theprecoding matrix is computed according to a minimum mean square error(MMSE) technique.
 42. The non-transitory computer-program product ofclaim 40, wherein the CQI comprises a signal-to-interference-plus-noiseratio (SINR) at each of the user terminals.
 43. A non-transitorycomputer-program product for signaling in a multiuser wirelesscommunication system with compact feedback, comprising a computerreadable medium having instructions stored thereon, the instructionsbeing executable by one or more processors and the instructionscomprising: instructions for estimating a channel between an accesspoint and a user terminal based on a received training sequence;instructions for performing a singular value decomposition to computeeigenvalues and eigenvectors of the estimated channel; instructions forselecting up to a specified number of most reliable eigenmodes to be fedback to the access point; instructions for receiving a precoded signalcomprising precoded data and a precoded training sequence; instructionsfor estimating the precoded channel gain using the precoded trainingsequence; and instructions for applying a spatial filter to the receivedprecoded data to recover a specified number of spatial streams dedicatedto each individual user terminal.
 44. A non-transitory computer-programproduct for signaling in a multiuser wireless communication system withhybrid feedback, comprising a computer readable medium havinginstructions stored thereon, the instructions being executable by one ormore processors and the instructions comprising: instructions forestimating full uplink channels based on a sounding sequences receivedfrom a plurality of user terminals; instructions for estimating adownlink channel between the access point and each of the user terminalsassuming reciprocity of corresponding uplink and downlink channels;instructions for computing eigenvalues and eigenvectors of estimateddownlink channels; instructions for selecting most reliable eigenmodesup to a predefined number per downlink channel between the access pointand each of the user terminals; instructions for generating a precodingmatrix based on computed selected eigenvectors, correspondingeigenvalues, and estimated channel quality information (CQI);instructions for sending a single spatial stream per user terminal thatcarries information regarding the number of spatial streams allocated tothat specific user terminal; instructions for performing preprocessingof data and of a preceding training sequence using the precoding matrix;and instructions for transmitting the precoded data preceded by theprecoded training sequence along with an indication of the number ofspatial streams to be processed at every user terminal.
 45. Thenon-transitory computer-program product of claim 44, wherein theprecoding matrix is generated using a minimum mean square error (MMSE)technique.
 46. The non-transitory computer-program product of claim 44,wherein the CQI comprises a signal-to-interference-plus-noise ratio(SINR) at every user terminal.
 47. A non-transitory computer-programproduct for signaling in a multiuser wireless communication system withhybrid feedback, comprising a computer readable medium havinginstructions stored thereon, the instructions being executable by one ormore processors and the instructions comprising: instructions fortransmitting a sounding sequence along with explicit data carrying aquantized version of estimated Channel Quality Information (CQI) at auser terminal; instructions for receiving a precoded signal;instructions for estimating a precoded channel gain using a precodedtraining sequence; and instructions for applying a spatial filter toreceived precoded data to recover a specified number of spatial streamsdedicated to the user terminal.
 48. A non-transitory computer-programproduct of claim 47, wherein the CQI comprises asignal-to-interference-plus-noise ratio (SINR) at the user terminal. 49.A non-transitory computer-program product for signaling in a multiuserwireless communication system with full feedback, comprising a computerreadable medium having instructions stored thereon, the instructionsbeing executable by one or more processors and the instructionscomprising: instructions for transmitting a predefined trainingsequence; instructions for computing eigenvalues and eigenvectors ofestimated downlink channels; instructions for selecting most reliableeigenmodes up to a predefined number per downlink channel between anaccess point and every individual user terminal; instructions forgenerating a precoding matrix based on computed selected eigenvectors,corresponding eigenvalues, and estimated channel quality information(CQI); instructions for sending a single spatial stream per userterminal that carries information regarding the number of spatialstreams allocated to that specific user terminal; instructions forperforming preprocessing of data and of a preceding training sequenceusing the precoding matrix; and instructions for transmitting precodeddata preceded by a precoded training sequence along with an indicationof the number of spatial streams to be processed at every user terminal.50. The non-transitory computer-program product of claim 49, wherein theprecoding matrix is generated using a minimum mean square error (MMSE)technique.
 51. The non-transitory computer-program product of claim 49,wherein the CQI comprises a signal-to-interference-plus-noise ratio(SINR) at every user terminal.
 52. A non-transitory computer-programproduct for signaling in a multiuser wireless communication system withfull feedback, comprising a computer readable medium having instructionsstored thereon, the instructions being executable by one or moreprocessors and the instructions comprising: instructions for estimatinga channel between an access point and a user terminal based on areceived training sequence; instructions for transmitting a quantizedversion of a normalized full downlink channel matrix and a quantizedversion of estimated channel quality information (CQI); instructions forreceiving a precoded training sequence; instructions for estimating aprecoded channel gain using the precoded training sequence; andinstructions for applying a spatial filter to received precoded data torecover a specified number of spatial streams dedicated to the userterminal.
 53. The non-transitory computer-program product of claim 52,wherein the CQI comprises a signal-to-interference-plus-noise ratio(SINR) at the user terminal.